The assessment of the ecotoxicological risks caused by pesticides to ecosystems is based on data on the toxicity and effects of pesticide preparations to non-target organisms. Fish are among the group of non-target aquatic organisms. Responses of aquatic organisms are broad-ranged depending on the toxic compound, exposure time, water quality and the species. Monocrotophos is one of the organophosphorous pesticide used in this study. The median lethal concentration (LC 50) of MC to fish L. rohita for 96 h was found to be 45.1 ppm. In sublethal concentration(1/10th of LC 50 96h value, 4.51ppm) fishes were exposed for 24, 48, 72 and 96 hrs, 10 days, 20 days and 30 days. Histopathological lesions were noted in the gills, liver and kidney when compared to the control.
